FR2724122A1 - Sewage settling tank with float-supported lid - Google Patents

Abstract

Circular sewage settling tank includes a decantation tank (1) contg. a central inlet (2) for the water; a sloping tank floor (10) between the central inlet (2) and the tank peripheral wall; and recovery means for water decanted at the peripheral wall (6). A slow-rotating bridge is positioned beneath the tank cover (18) and around the central inlet (2) to direct settled solids across the sloping tank floor (10). The settling tank is improved in that the cover (18) is composed of laminated segments (17,20) whereby each segment has a stationery float (18) to support it. Floats (32) are spaced circumferentially around the lid allowing water to flow between them.

Description

 The present invention relates to a large diameter settling tank intended for the treatment of loaded waste water, in particular capable of separating by gravity the water and the residues.

 It will find its application in particular in the field of construction of water settling facilities which can be carried out on a municipal, regional or private industrial scale.

 I1 exist in all industrial fields very many applications of water decantation and we therefore very often need to build settling tanks which have large diameters because they must be able to treat a very large volume of water.

 Thus, for example, when these charged waste water comes from the production of a high capacity factory, it is necessary to have very large diameter basins which can be included very regularly between forty and eighty meters. Beyond this size, it is sometimes even necessary to build several settling tanks to absorb all of the loaded wastewater.

 These settling tanks which are heavy investments are therefore made robustly with a construction in solid masonry. Different decantation techniques are used today but when it comes to gravity separation of water and residues in a large-diameter basin, we generally accept the water to be treated by a central sump located in the middle of tank.

A circular peripheral veil is built around the central sump to collect around the tank the clean treated water which is separated by gravity from the residues.

 This operation is carried out in a very large tank and the waste water admitted to the tank at the sump must remain in this tank for a long time to undergo the desired decantation. This decantation must take place in a slow regime and must therefore avoid any mixing, turbulence or vortex which would have the effect of opposing the slow decantation of the particles.

 The waste water which is admitted to the center of the tank in several zones will therefore circulate gently towards the outside of the tank and the treated clean water will be collected by overflow at a chute located on the peripheral veil of the tank. This recovery will only be carried out after a long stay of the water in the tank over the entire distance between the center and the periphery, which is often several tens of meters.

 Known basins also include to facilitate their settling a slope between the sump and the veil and this slope which constitutes the bottom of the basin generally has a truncated cone shape. Thus, the tank is deeper in its central part than in the periphery to facilitate decantation.

 In the deepest part of the tank and at the base of the central sump are generally arranged means for recovering the solid residues which have been decanted. As soon as the residues reach the bottom of the tank, they can flow on the slope of greatest length and this to the recovery means located in the deepest area.

 The separation between water and residues is done by a purely physical phenomenon of gravity and the particles in suspension in the water agglutinate to become heavy before depositing on the bottom. To avoid a too large accumulation of particles on the bottom, a rotary bridge is made in a known manner in the settling basins which is generally secured at one end of the central sump and which rests on the peripheral veil by means of bearings such as for example pebbles. This bridge is driven in a known manner in rotation around the central sump and generally very low displacement speeds are used for it so as naturally not to disturb the settling by turbulence or eddy phenomena. We have thus obtained good results in pools of forty to eighty meters by rotating the bridge at a speed of the order of one revolution per hour.

 On the revolving bridge, a base blade is generally fitted at its base which allows scraping of sludge at low speed. The scraping of the sludge and the slope of the tank generally make it possible to recover, under good conditions, the solid residues at the foot of the central sump.

 Settling ponds functioning in this way have so far given good results with regard to decanting proper. However, the basins known today have a surface of water in the open air, which has significant drawbacks when the treated products are particularly fragrant or when they attract animals and for example gulls.

 Serious operating difficulties have therefore arisen today in the development of settling basins which, in most cases, are very odorless and the solutions which could have been developed on this subject have not given satisfaction today. hui.

 We have for example thought, to reduce odors, to place the entire settling tank under a giant bubble to isolate the stale air to be treated.

 This solution nevertheless has serious drawbacks because the volume of air to be treated is very large, which leads at the time of implementation to very high prices, especially when this is applied to large pools and in particular from forty to eighty meters in diameter.

 Another disadvantage of the giant bubble is that the personnel inside the bubble work in a contaminated atmosphere that is difficult to breathe.

 The stale air which is also captured in the bubble is generally very corrosive since the odorous air very often contains sulfur dioxide which in a hzzid medium leads to the formation of weakly diluted sulfuric acid which is very corrosive for electrical mechanisms and contacts.

 In these large-diameter basins, it is also not possible to install a pole in the middle of the basin resting on the bottom to support the structure of the bubble and reduce its size. Indeed, it is necessary to have a single span for the structures covering the large settling basins because the presence of support posts in the middle of the basin would prevent settling in good conditions or the passage of the revolving bridge at slow speed .

 The present invention aims to remedy these drawbacks and for this purpose, one of the first purposes of the large-diameter settling tank intended for the treatment of waste water is to effect good decantation by working at very slow speed so as not to disturb the decantation. on the order of one revolution per hour on average.

 Another advantage of the large diameter settling tank intended for the treatment of waste water according to the invention is to be able to cover the works and in particular the tank for capturing stale air. It can then be treated since it is trapped between the surface of the water and the cover.

 Another object of the large-diameter settling tank intended for the treatment of waste water according to the invention is to reduce the volume of air between the surface of the treated water and the cover to make the deodorization operation possible because the dirty and smelly air is expensive to treat.

 Another object of the large-diameter settling tank intended for the treatment of waste water according to the invention is not to create turbulence or vortex in the water to be treated to improve the settling.

 Another advantage of the large-diameter settling tank intended for the treatment of waste water according to the invention is to produce the elements of the cover in a resistant material having a load-bearing structure despite the large dimensions of the tank, for example between forty and eighty meters of diameter.

 Another object of the large-diameter settling tank intended for the treatment of waste water according to the invention is to provide on the load-bearing elements of the cover of the floats to support the elements, non-submerged floats to avoid vortexes and turbulence which harm the decantation.

 Another advantage of the large-diameter settling tank intended for the treatment of waste water according to the invention is that the floats are not immersed in order to reduce the wear of the peripheral rollers and reduce the support of these rollers on the concrete structure of the web. peripheral.

 Another object of the large diameter settling tank intended for the treatment of waste water according to the invention is to provide elements of the cover designed with a resistant but light structure on which is fixed an impermeable textile coating making it possible to reduce the cost price of the cover and withstand the weight of snow.

 Another object of the large diameter settling tank intended for the treatment of waste water according to the invention is to use floats which are not completely submerged when the rollers turn on the peripheral web. This arrangement makes it possible to relieve the work of the rollers in the event of overload, for example by snow.

 Another advantage of the large-diameter settling tank intended for the treatment of waste water according to the invention is that the cover elements are designed in their structure, wooden frame, glued laminated sheet covered with an impermeable material of low weight to produce a self-contained cover. -bearing in large constructions but also with a fairly low weight which will be useful because it will be driven by the rotation of the swing bridge.

The present invention relates to a large diameter settling tank intended for the treatment of loaded waste water, capable of separating by gravity the water and the residues, more particularly usable when it is desired to reduce the odors and treat the air between the water surface and the cover, comprising
A. a settling tank with
- a fixed central sump into which water is admitted
treat,
- a circular peripheral veil around the sump
central,
- a slope between the sump and the veil constituting the
bottom of the basin in the shape of a truncated cone,
means for recovering the solid residues decanted at
the base of the central sump,
- means to recover decanted water at the level
peripheral veil,
B. A rotating bridge secured to the central sump and which
rests on the peripheral veil by means of bearings
which allow the movement of the bridge at low speed, characterized in that it has
C. a cover of the mobile tank with the bridge made at
from a multitude of radial elements each taking
support on the one hand on the central float of the sump and
on the other hand on the float,
D. each element of the cover is produced in a
load-bearing laminated structure on which is
placed a satellite float partially submerged in
the water to be treated in order to support the entire cover
and to relieve the bearings of the peripheral veil, in order to reduce the volume of stale air between the surface of the water and the elements of the cover so as to permanently deodorize it.

The invention will be better understood by referring to the following description of a non-limiting embodiment, illustrated by the accompanying drawings in which
FIG. 1 is a partial section view of the large-diameter settling tank according to the invention,
FIG. 2 is a partial view of the basin seen from above,
- Figure 3 is a detailed sectional view of the periphery of the basin.

 Reference is made to FIG. 1 which shows a partial sectional view of a large diameter settling tank intended for the treatment of loaded waste water.

By fillers is meant any manufacturing residue or pollutant which it is desired to separate from the water for the purpose of recycling or treatment before discharge.

 These basins can therefore be used for the settling of urban waters but also industrial waters in a very broad way because there are many applications in the paper and chemical industries.

 The settling tanks which are generally built today can have a diameter of between forty and eighty meters because they must contain a large volume so that their treatment capacity is not negligible but they must also slowly treat the loaded waste water. because the decanting operation is not an immediate phenomenon even if it is carried out by gravity.

 The present invention is particularly applicable to large-diameter settling tanks which will have to solve pollution or odor problems and therefore which will have the objective of treating the air which is released from the charged waste water contained in the tank.

 The basin is constituted by the actual tank (1) of large dimension, for example made of masonry or concrete. The tank comprises in a known manner a fixed central sump (2) into which the charged waste water to be treated is admitted, which flows in the direction of the arrow (3). The sump (2) comprises, in a known manner, numerous orifices (4 and 5) allowing the flow of the water to be treated in the direction of the arrows F, that is to say to allow the progression of the water from the central sump (2) to the peripheral veil (6). This veil, generally circular, is several tens of meters from the central zone (2) and it is arranged in a known manner to include a chute. (7) which constitutes the means for recovering the decanted water at the level of the peripheral veil and this by overflowing of the surface (8) which comes flush with the end (9) of the chute (7).

 Between the veil (6) and the sump (2), a slope (10) of several tens of meters is advantageously made of concrete or another material suitable for the settling carried out. This slope (10) has the shape of a truncated cone and the height H of the center of the tank is greater than the height h of the periphery of the tank.

This slope is naturally also calculated according to the operations to be carried out and in particular the decantation and the residues to be treated.

 The slope (10) is extended at its end (11) in the central zone of the tank by a chute (12) which constitutes the means for recovering the settled solid residues such as sludge (13).

 When the materials and aggregates contained in the loaded wastewater have been able to come together during decantation and that they have reached a critical size or mass, the loaded materials may then fall naturally by gravity into the bottom of the tank and constitute, for example, a muddy area (14) on the slope (10) of the tank.

 In a known manner in the settling tank according to the invention, it is possible to use a rotary bridge (not shown) which can be secured to the sump (2) and which will also rest on the peripheral veil (6) for example on the path bearing (15) by means of rollers and rollers not shown.

 This arrangement will ensure, in a known manner, the movement of the revolving bridge at slow speed around the axis (16). On this bridge, a bottom blade will have been suspended which will allow scraping of the sludge (14) located in the slope (10). It is the movement of this bridge at very slow speed which, after the settling of the sludge, will ensure their displacement from the entire surface of the basin to the central area and towards the trough (12) where the separated sludge will be collected.

 If, during decantation, it is necessary to transport the sludge, it must be done at very slow speed because simultaneously, decantation throughout the volume of the basin must continue. Do not create turbulence or a vortex that could disturb it.

 FIG. 1 shows a cover generally designated by (17) which firstly makes it possible to isolate in a volume V the air contained between the surface of the water (8) and the wall (18) of the cover. . We tried to reduce this volume to the maximum because we know that the treatment of stale air is expensive, this is why the upper part (18) of the cover is very flat despite the large dimension of the diameter of the basin of the order from forty to eighty meters. It is then possible by means of the conduit (19) to send this stale air to a central deodorization.

 Because of the very large capacity of the tanks, we preferred to cut the cover into several elements such as (17 and 20) shown in Figure 2. We can, depending on the size of the basin, choose to cut the cover into sixteen elements such as shown. The sixteen elements, such as (17) will all be identical and they will cover the entire tank (1).

 Referring to Figure 1, we see that the end (21) of an element (17) rests on a central float (22) arranged on the sump (2). The other end (23) of the element (17) which is distant by several tens of meters from the end (21) is constructed with a wheel (24) which will be able to move on the path (15) of the peripheral veil (6). It should be noted that in a normal position shown in Figures 1 and 3, the wheel (24) does not come into contact with the path (15), which allows during the operation of the swing bridge, to save the wheels (24 ).

 In a normal situation of use, the absence of contact of all the wheels (24) with the track (15) prevents braking of the rotary bridge. These wheels (24) nevertheless constitute a safety device if additional pressure were to be exerted in the direction of the arrow P, which would cause the wheels (24) to roll along the path (15). This force in the direction of arrow P can for example be caused by a thickness of snow likely to come to deposit on the cover (18).

 Reference is made to FIG. 2 which shows that the elements (17 and 20) of two support beams (25 and 26) with a secondary beam (27). By beam is meant a thin construction, preferably of glued laminated wood, the profile of which is shown in FIG. 1 with a base (28) substantially horizontal and two inclined zones (29 and 30). The supporting beams (25 and 26) as well as the secondary beam are preferably made of a rigid material making it possible to reach supporting structures over significant distances corresponding to the diameter of the settling tank between forty and eighty meters. For a tank of forty meters, we have thus obtained good results with a glued laminated beam of the following dimensions: 460-790-260.

 It was also possible with these forms of beams to produce a very flat cover by assembling the elements (17). This flat cover reduces the volume V.

 The central sump (2) is made as a central float (22) which supports the ends (21) of each element (17) of the cover. On each element (17) of the cover, satellite floats (32) have been fixed at (31). It should be noted that each of the floats is independent and that they do not constitute a continuous flotation surface since the water can for example flow between each float in the direction of arrow 33.

 The relative arrangement of the floats and their design make it possible to avoid too much turbulence on the surface of the water (8) and, for example, floats (32) have preferably been produced with an immersed area (34) but also not submerged (35). It should be noted in fact that too much immersion of the floats (32) would have the consequence of creating turbulence and vortices in the water and therefore of harming, as we have seen, good decantation. The height (35) of the non-submerged part of the floats corresponds substantially to the distance between the roller (24) and the safety tread (15) in order to collect the thicknesses of snow or thrusts in the direction of the arrow P.

 Advantageously, floats (32) have been produced which can be oriented around their axis (31) to adjust the acceleration of the surface water. Figure 2 shows a float (32) with asymmetrical parts (36 and 37) allowing adjustment of the orientation.

 Each element of the cover (17 and 20) is produced in a load-bearing framework, preferably made of glued laminate. Between each beam (25 and 26) is placed a textile covering over the entire distance corresponding to the diameter of the basin. This coating may be made of a textile or synthetic material, for example a canvas which has the advantage of being light and resistant. In certain applications, the canvas may also be waterproof. It will be noted that the elements of the cover, beams and covering are designed to give satisfaction as a support structure but that they must be light enough not to slow down the movement of the rotary bridge in the direction of the arrow (39). The floats (32) make it possible to support as a whole various elements of the cover by creating the least turbulence on the surface of the water and by making it possible to reduce the volume of air as much as possible for large basins.

 We can also set up a canvas stretched in one piece on all the secondary and load-bearing beams on the 360 "of the cover, which can be an advantage in certain constructions to obtain a fairly hermetic volume V.

 Naturally, other implementations of the present invention, within the reach of those skilled in the art, could also have been envisaged without departing from the scope thereof.

Claims (5)

 1. Large diameter settling tank intended for the treatment of laden waste water, capable of separating by gravity water and residues, more particularly usable when it is desired to reduce odors and treat the air between the surface of the water and cover, including A. a settling tank (I) with  - a fixed central sump (2) into which water is admitted  treat,  - a circular peripheral veil (6) around the sump  central (2),  - a slope (10) between the sump (2) and the veil (6)  constituting the bottom of the basin in the form of a truncated cone,  means for recovering the solid residues decanted at  the base of the central sump (2),  - means to recover decanted water at the level  peripheral veil (6), B. A rotary bridge secured to the central sump (2) and  which rests on the peripheral veil (6) by means of  bearings that allow the speed bridge to move  slow, characterized by the fact that it presents C. a cover (18) of the movable tank with the bridge  made from a multitude of radial elements (17,  20) each taking support on the one hand on the float  central (22) of the sump (2) and on the other hand on the  float, D. each element (17) of the cover is produced in a  load-bearing laminated structure on which is  arranged a partially submerged satellite float (32)  in the water to be treated in order to support the entire  cover and relieve the bearings (15) from the veil  device (6), in order to reduce the volume of stale air between the surface of the water and the elements of the cover in order to permanently deodorize it.  2. Large-diameter settling tank intended for the treatment of loaded waste water, capable of separating by gravity the water and the residues, more particularly usable when it is desired to reduce odors and treat the air between the surface of the water and the cover according to claim 1, characterized in that the floats (32) have a variable angulation constituted by the asymmetrical sides (36 and 37).  3. Large diameter settling tank intended for the treatment of laden waste water, capable of separating by gravity the water and the residues, more particularly usable when it is desired to reduce odors and treat the air between the surface of the water and the cover according to claim 1, characterized in that the floats (32) are orientable.  4. Large diameter settling tank intended for the treatment of charged waste water, capable of separating by gravity water and residues, more particularly usable when it is desired to reduce odors and treat the air between the surface of the water and the cover, according to claim 1, characterized in that each element (17) of the cover (18) is produced from two load-bearing beams (25, 26) and a secondary beam (27) on the half the diameter of the pool, an impermeable textile covering being secured to each element.  5. Large diameter settling tank intended for the treatment of loaded waste water, capable of separating by gravity water and residues, more particularly usable when it is desired to reduce odors and treat the air between the surface of the water and the cover according to claim 1, characterized in that the fabric is stretched in one piece above.